An elevator typically comprises an elevator shaft into which an elevator car and/or a counterweight are arranged vertically movable, a driving unit with which the elevator car is moved. The driving unit may comprise a motor and a driven rope wheel engaging elevator suspension or hoisting roping. The roping is arranged between elevator car and the counterweight. The driving force of the motor is transmitted to the car via the driven rope wheel.
In addition, there may be one or more stationary pulley wheels, mounted in the proximity of the upper end of the elevator shaft, for guiding and aligning the suspension roping along the vertical direction of the elevator shaft. In some cases, there may also be additional second roping between the elevator car and the counterweight, suspended to hang from the elevator car and the counterweight, to provide compensation for the weight of the suspension roping. The second roping may also provide a lock-down function. The second roping may be tensioned to pass around one or more second pulley wheels mounted stationary in a position below the elevator car and the counterweight, typically in the lower end of the elevator shaft.
A pulley wheel may be mounted in a pulley wheel space delimited by two supporting walls formed by a pulley wheel rack or frame. The pulley wheel is supported on the rack via an axle with two ends, one end being supported by one supporting wall and the other by the other supporting wall. The pulley wheel rack may be fixedly mounded on a suitable space, typically inside the upper end of the elevator shaft or inside a machine room of the elevator, above or adjacent to the elevator shaft. The pulley wheel rack may for example be mounted on the motor bedplate. One or more of the pulley wheels may be the driven rope wheel.
The elevator rope or ropes must be carefully aligned and guided between consecutive pulley wheels to ensure that the rope does not twist excessively when travelling from one pulley wheel to another, and that the rope arrives at and departs from the traction surface of a pulley wheel at least substantially tangentially. Typically, this alignment operation is done by adjusting the position of the pulley wheel rack by adjusting screws, or by shimming plates. With screws, the midpoint of the pulley wheel may easily move away from its initial position. With shimming plates, the pulley wheel may have to be raised several times until a proper position is achieved, which is not only time consuming but also involves heavy lifting work.
Aligning the elevator ropes by aligning the pulley wheels may be an extensive operation for technicians responsible for the installation and/or maintenance of an elevator. Especially in installations where several pulley wheels must be aligned, each one in both tilt and toe directions, i.e. in camber and caster, so that the rope is guided to move in the middle of the traction surface of the pulley wheel. The aligning must be done with great care, since an inadequately aligned rope may run asymmetrically causing the rope to wear in an unexpected and wrong way. The rope may even move away from the traction surface during operation of the elevator. The alignment must be done every time one or more of the ropes are changed, or when other maintenance work is performed that would affect the roping of the elevator.